Although the legal drinking age in the United States is age 21, underage drinking is highly prevalent, even normative. Early onset of alcohol use is associated with increased risk of a number of subsequent maladaptive outcomes, including heavy or problem drinking, likelihood of developing an alcohol use disorder, other substance involvement, and behavioral problems. However, early course of drinking among underage drinkers has been relatively understudied. The goal of this application is to explore characteristics of the early drinking career including sequencing of and progression through drinking-related milestones such as first drink, first time drunk, first regular drinking, first binge drinking, and first experience of an alcohol-related problem. In addition, although it is likely that early drinking course differs for those with early versus late onset, the nature of this association is unclear. Consistent with problem behavior theory and work showing common vulnerability to early initiation and subsequent alcohol involvement, early onset individuals may have a more rapid progression to problematic alcohol use and related problems. In contrast, early onset individuals may progress more slowly due to the limited social and physical availability of alcohol. This research project will conduct analysis of drinking course in early- to mid- adolescence using three secondary datasets, including the National Longitudinal Study of Adolescent Health (AddHealth), the National Longitudinal Survey of Youth (NLSY97), and the Drug Abuse Treatment Outcome Study for Adolescents (DATOS-A). Two of these datasets are nationally representative prospective samples and the third is a treatment sample which has a rich assessment of age of initiation of different milestones. The different characteristics of the three datasets permit resolution of specific questions that play to the strengths of each dataset. In addition, by using a clinical treatment sample, we can depict drinking course among a high-risk sample who has already initiated heavy drinking which will complement findings using two general population samples primarily comprised of adolescents whose drinking is at a very early and non-risky stage. Specific aims of the proposed study are to explore normative as well as inter- and intra-individual variation in velocity of progression through early drinking milestones, and to examine the association of early drinking course with exogenous, endogenous, grouping, And confounding variables using techniques of item response theory modeling, survival analysis, and latent transition analysis. When these specific aims are met, we will better be able to understand the prognostic significance of age of first drink and we will be closer to understanding whether youth who show early risky drinking differ from the general population with regard to their experience with various early drinking milestones. [unreadable] [unreadable] [unreadable]